From experience now:

I did several tests to record audio on the TYROS2, with my older Harddisk from Tyros1.
I did not realize it was an 4200 RPM HD, one MB buffer memory.
I could record as well as mix new record with existing track as well as replay audio without problems on this harddisk.

One of the TOP demonstrators of Yamaha very told me he has build his older T1 5200 RPM disk into the T2 and had no problems at all, and was very confident a recent 5200 RPM disk is sufficient.

If somebody now tells me disasters when I dont take a 7200RPM disk, I strongly tend not to believe him, also price and noise is higher.

Cheers JaapV (nl)